Tom -
Thanks for your reply. I was not present during the testing. In my opinion, and now I have been able to convince others, the contractor passed the test, which is derived from MIL-STD-118-164ACN2. The main specification states the following: 5.1.2.5 Carrier frequency accuracy. The carrier frequency accuracy at the antenna feed shall be within 1 KHz of the intended value for all RF carriers. Recalibration intervals to maintain this accuracy shall not be less than 90 days. This is on an Army satellite terminal. Another branch of the Army came up with the 11 Hz requirement over 24 hours (for testing purposes), which is just 1KHz/90, and I feel it is total rubbish. I myself have been trying to find out the gate time used on the counter, but have not been abler to get it yet and not sure I will. Needles to say, using the stated counter, and logging a measurement at one minute intervals with a resulting readout down to 1 Hz at 30 GHz, probably does not leave too many options for gate time. The jumps do not exactly come in pairs, although they seem to, but, remember there are close to 16,000 points on that graph. I agree with you that averaging would make the plot into a straight line. During the testing this terminal was in California, outside, so the temperature extremes were just the day to night extremes and relatively slow respect to time. I doubt if they knew the sats-in-view, but I will ask, and I am certain that they have no idea about DOP, and I am not sure how that would affect the frequency measured. I pointed out about 6 months ago that I did not like where they had their GPS antenna mounted as it was, at times, blocked by the 2.4 meter reflector. They do believe that at times they lost some birds and since re-located the GPS antenna. I did contact John Vig about this, however at this time he is too busy with his activities as President elect of the IEEE, a post which he will take in 2009. He also retired from the Army in 2006. He did give me another contact within the Army, Ray Filler, and Ray is in agreement with all of my assumptions and conclusions, and is in the process of reading a white paper on the subject that I wrote. I was just hoping to get some ideas from this august group, hence the reason for my post. I will let you know if I find out anything else. BTW, loopback testing on the terminal at threshold Eb/No yielded the desired BER without any synch losses over a 24 hour period. Thanks & Regards - Mike Mike B. Feher, N4FS 89 Arnold Blvd. Howell, NJ, 07731 732-886-5960 -----Original Message----- From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf Of Tom Van Baak Sent: Tuesday, October 14, 2008 3:38 PM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] Frequency Stability of Trimble Mini-T Mike, I keep hoping to find a Mini-T on eBay but no luck yet and so I don't have plots on my web site for that unit. Does anyone have a loaner? Question on the spec and on your plot, though. What is the gate time of the frequency measurements? If you average for an hour or a day many of those peaks would melt. Also most look like phase jumps not frequency jumps. When you see frequency jump up and then down by the same amount as a pair it's usually the result of a single phase jump. Did you log sats-in-view, or DOP, or temp during your run to see if the jumps correlated to that? Finally, "frequency drift" is not at all the same thing as "frequency excursions", so what did they really mean? /tvb > The attached URL is a 11 day plot of a 30.5 GHz carrier taken every minute > by an Agilent 53152A microwave counter. The Mini-T has an ovenized > oscillator. It appears that the GPS attempts to over correct the oscillator, > hence the large frequency excursions. The real large excursions, around the > 96 hour range, were due to a loose connector. The requirements are such that > over a 90 day period the total frequency drift shall be no more than 1 KHz. > Someone in their ultimate wisdom, decided that since they do not have the > time to take measurements for 90 days, they will take it for 24 hours and > not allow any frequency excursions over 11 Hz at 30.5 GHz. Obviously, this > plot does not pass their requirement. When the oscillator is allowed to free > run, the frequency jumps are not there. Has any one else made any > measurements on the Trimble Mini-T. Any observations or suggestions are > appreciated. Regards - Mike > > http://www.eozinc.com/11dayplot.pdf > > > Mike B. Feher, N4FS > 89 Arnold Blvd. > Howell, NJ, 07731 > 732-886-5960 _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
